The present invention relates to an apparatus for reproducing image signals recorded on a magnetic tape, and relates more particularly to an apparatus having several different modes for running a magnetic tape. According to the present invention, it is also possible to have a unit for recording image signals and audio signals on a magnetic tape.
In recent years, time lapse video tape recorders (VTR) have been widely used which can intermittently record image signals on a normal video tape that is commercially available, such as, for example, the VTR's which can record image signals over 720 hours on one video tape. These VTR's are being used for mainly recording image signals sent from monitoring television cameras at, for example, plants, construction fields, stores, etc. When some abnormal incidence has occurred at these places, it is possible to obtain valuable information by reproducing image signals that have been recorded by these VTR'S.
One example of such a conventional time lapse VTR as mentioned above will be explained in further detail with reference to drawings.
FIG. 24 is a block diagram for showing one example of the conventional time lapse VTR. 7 designates a system control unit that produces a normal mode pulse Ma, a continuous slow mode pulse Mb and an intermittent mode pulse Mc, in a normal mode for running a magnetic tape of the time lapse VTR at a normal speed, a continuous slow mode for running a magnetic tape of the time lapse VTR at the speed of 1/n of the normal running speed (where n is a natural number) and an intermittent mode for intermittently running a magnetic tape respectively. The system control unit 7 also produces an operation mode selecting signal MS for selecting a mode pulse corresponding to any one of the normal driving mode, the continuous slow driving mode and the intermittent driving mode.
20 to 23 designate magnetic heads and 19 designates a rotating cylinder. In the rotating cylinder 19, the magnetic head 23 having a second azimuthal angle is disposed at an angular position of 180 degrees from the position of the magnetic head 20 having a first azimuthal angle, the magnetic head 21 having a second azimuthal angle is disposed adjacent to the magnetic head 20, and the magnetic head 22 having a first azimuthal angle is disposed at an angular position of 180 degrees from the position of the magnetic head 21. The adjacent magnetic heads 20 and 21 and magnetic heads 22 and 23 respectively form double azimuth heads. The rotating cylinder 19 having this structure will hereinafter be referred to as a DA-4 structure cylinder. The first azimuth and the second azimuth will hereinafter be referred to as a plus azimuth and a minus azimuth respectively.
The system control unit 7 produces an SW 30 pulse which discriminates a recording and reproducing period between the period when recording and reproducing is being carried out by keeping the magnetic heads 20 and 21 in contact with a magnetic tape 18 that is run by being wound around the rotating cylinder 19 and the period when recording and reproducing is being carried out by keeping the magnetic heads 22 and 23 in contact with the magnetic tape 18 which is run by being wound around the rotating cylinder 19.
A servo circuit 10 is used for driving a capstan motor 14 and a cylinder motor 15, and this servo motor 10 can change over between the driving modes of these two motors based on an operation mode selecting signal MS. 2 designates an image signal processing unit, 28 designates an aural signal recording and reproducing unit, 11 designates a control (CTL) change over switch for changing over between a recording CTL signal and a reproducing CTL signal, and 12 designates a control unit for controlling recording and reproducing of CTL signals.
5 designates an added vertical synchronizing signal (hereinafter to be referred to as an AVSS) unit, which is structured by an AVSS change over switch 5a for changing over between the case of fitting an AVSS and the case of not fitting an AVSS, an AVSS refitting unit 5a for changing the fitting of an AVSS on behalf of the AVSS in an image signal that has been reproduced, and an AVSS producing unit 5c for producing the AVSS.
4 designates a recording and reproducing control unit, which is structured by a recording circuit 4a, a recording and reproducing change over switch 4b for changing over between a recording time and a reproducing time, a magnetic head change over switch 4c for changing over between the magnetic heads for reproducing images based on the SW 30 pulse, an azimuth change over switch 4d for changing over the reproducing magnetic heads of corresponding azimuthal angle based on an azimuth change over pulse AZP, and an amplifier circuit 4e. 24 designates a CTL head for recording and reproducing a CTL signal, 25 a pinch roller, 26 a capstan, 16 a supply reel, 17 a winding reel, 27 an aural magnetic head for recording and reproducing an aural signal, 28 an aural signal recording and reproducing unit, and 13 an azimuth pulse change over switch for changing over an azimuth change over pulse between AZP' and AZP at the time of the normal and intermittent reproduction driving modes and the continuous slow reproduction driving mode respectively. 29 designate an input terminal for inputting a recording aural signal and 30 designates an output terminal for outputting a reproduced aural signal.
33 designates an azimuth selecting unit, which is structured by comparing and deciding circuits 33b and 33c that decide a larger output that is produced from the magnetic heads 20 and 21 and from the magnetic heads 22 and 23 respectively, and a comparison and decision change over switch 33a for selecting an output from the comparing and deciding circuits 33b and 33c based on the SW 30 pulse. At the time of a continuous slow mode reproduction, the azimuth selecting unit 33 outputs the azimuth change over pulse AZP for selecting always a larger output of the image signal reproduced from a magnetic head out of the magnetic heads of different azimuthal angles of the double azimuth heads, and changes over between the azimuths of the magnetic heads of different azimuthal angles.
A tape guide for winding the magnetic tape 18 around the rotating cylinder 19 and a motor for operating the reels and pinch roller are not shown in the drawings.
With the above-described structure, when a commercially available 120-minute video tape is used, it is possible to achieve a long-time recording, such as, for example, a 2-hour recording in the normal run standard mode of the VHS system VTR (an sp mode, a track width 59 .mu.m), and 24 hours, 120 hours and 480 hours, etc. both in the continuous slow driving mode in which the rotation speed of the capstan motor 13 is dropped and in the intermittent driving mode. Similarly, a long-time recording can also be achieved in a three time long-time mode of the capstan 14 that runs at a speed slower than the speed of the standard sp mode (an EP mode, a track width 19.3 .mu.m).
The operation of the continuous slow driving mode in the time lapse VTR of the above-described structure will be explained below.
When the rotating cylinder 19 of the DA-4 structure rotates, the magnetic heads 20 to 23 sequentially trace the tracks of different azimuthal angles (hereinafter to be referred to as azimuth tracks) on which image signals have been recorded on the magnetic tape 18, and reproduce the image signals. In this case, the +(plus) azimuth head 20 and the--(minus) azimuth head 21 and the +(plus) azimuth head 22 and the -(minus) azimuth head 23 have been disposed mutually adjacent to each other respectively to form double azimuth heads, and image signals are reproduced simultaneously by the mutually adjacent +azimuth head and the-azimuth head from the same track. Output levels of the image signals that have been reproduced simultaneously by the two magnetic heads of different azimuth polarities are compared and judged by the comparing and deciding circuits 33b and 33c respectively. The azimuth change over pulse AZP for selecting a magnetic head of the azimuthal angle of which output is larger than that of the other magnetic head is supplied to the azimuth change over switch 4d. During a continuous slow reproduction mode, a magnetic head of the azimuthal angle with a larger output is always being selected out of the double azimuth heads.
To be more specific, when the +azimuth portion is larger in an azimuth track that is being traced, the +azimuth head is selected automatically. On the other hand, when the--azimuth portion is larger in an azimuth track that is being traced, the--azimuth head is selected automatically. With this arrangement, the magnetic head of the azimuthal angle of which output is larger is always being selected. Accordingly, when a continuous slow reproduction is to be carried out by using a magnetic tape on which signals have been recorded in different recording modes, for example, it is possible to improve the problem of an output deterioration due to a state that the azimuth track can not trace the track correctly (a tracking failure), to thereby obtain a screen image with little tracking noise.
As described above, according to the conventional time lapse VTR, in reproducing an image in a continuous slow mode, an image signal of a larger output has always been selectively produced out of the image signals reproduced by the double azimuth heads. This method, however, has the following drawbacks.
FIG. 25 shows a state that magnetic heads are tracing azimuth tracks to reproduce image signals from a magnetic tape on which the image signals have been recorded in a recording mode other than a continuous slow recording mode. In FIG. 25, +VTa, +VTb and +VTc show +azimuth tracks, -VTa, -VTb and -VTc show--azimuth tracks and 109 to 112 designate magnetic heads which are tracing the azimuth tracks. Since the operating modes are different between the recording time and the reproducing time, the tracks of the magnetic heads for tracing the azimuth tracks are not parallel. In the drawing, an arrow X indicates a direction in which the magnetic tape is proceeding and an arrow Y indicates a direction in which the magnetic heads are tracing the tracks.
Referring to FIG. 25, if a magnetic head starts tracing the tracks in the state as shown by 111, the +azimuth head is selected out of the double azimuth heads and an image signal is reproduced from a right-downward shaded portion. When the tracing is continued to reach the state as shown by 112, the +azimuth head is still kept being selected to achieve a satisfactory reproduction.
On the other hand, when the tracing has started in the state as shown by 109, the output is larger from the +azimuth head at the beginning and therefore the +azimuth head is selected out of the double azimuth heads. However, at the state as shown by 110, the output becomes larger from the--azimuth head and thus the +azimuth head is changed over to the -azimuth head in the middle of the tracing, to reproduce an image from a right-upward shaded portion. This change over is carried out momentarily and the image signal level is always being kept to be large so that no tracking noise occurs.
However, in the middle of tracing an azimuth track, a magnetic head momentarily crosses over an azimuth track to a separate azimuth track and the magnetic head starts reproducing an image signal from the middle of this changed azimuth track. Accordingly, there is a risk that the reproducing timing of a horizontal synchronizing signal is deviated at this moment. At present, a signal processing utilizing an inter-line correlation is being carried out for every one H (where H is a horizontal scanning line) in the color VHS system and color S-VHS system respectively. Accordingly, there has been a problem that a signal processing can not be carried out in a normal condition when a reproduced H timing has deviated, resulting in an occurrence of a color noise in a lateral direction of the screen.
Further, there has been a problem that a screen fluctuation occurs due to a deviation of a synchronizing signal by a few H components at the moment when the track has changed from the +azimuth track to the -azimuth track or vice versa in the middle of the reproduction. In the case of reproducing an image signal in the intermittent reproduction mode, a magnetic head to be selected for the reproduction is known in advance and a magnetic head will not be changed over to a magnetic head of a different azimuthal angle until when the magnetic head has finished tracing one azimuth track. Accordingly, a method for correcting the deviation of H has been taken by adding an added vertical synchronizing signal to a reproduced image signal according to the selection of the magnetic head. However, in the case of reproducing an image signal in the continuous slow mode, it is not firm in advance which one of the magnetic heads of different azimuth angles is to be selected out of the double azimuth heads. Further, it is very difficult to predict a magnetic head to be used and to correct a deviation of H because a magnetic head is changed over to a separate magnetic head of a different azimuthal angle while the magnetic head is being tracing an azimuth track. Accordingly, no correction has been able to be made in the past when reproducing an image signal in the continuous slow mode.
The above problem also occurs when an image signal recorded on a magnetic tape in the continuous slow mode is to be reproduced in the continuous slow mode, or when the azimuth tracks are parallel with the tracks of the magnetic heads. This will be explained with reference to FIG. 26. In FIG. 26, 113 and 114 show magnetic heads which are tracing azimuth tracks.
Referring to FIG. 26, in tracing the azimuth tracks as shown by 113, the +azimuth head is selected to achieve a satisfactory reproduction of an image signal. When image reproduction is continued in this state, the magnetic head is not changed over from one to another magnetic head in the middle of the tracing so that a satisfactory reproduction can be continued. However, in actual practice, a position from which each magnetic head starts tracing each azimuth track is gradually deviated little by little from the other starting points due to a slight gap between the rotation of the capstan motor 14 and the phase of the cylinder motor 15.
As a result, when the same magnetic head comes to trace a half of the +azimuth track and a half of the -azimuth track as shown by 114, the output level of the +azimuth head becomes almost the same as the output level of the -azimuth head, so that both the +azimuth head and the -azimuth head come to be selected alternately in the middle of the tracing of the azimuth tracks due to a slight variation between the rotation of the capstan motor 14 and the rotation of the cylinder head 15. Because of this change of an azimuth head selected, a color noise momentarily occurs on the screen each time when a magnetic head is momentarily changed over to a magnetic head of a different azimuthal angle across the azimuth tracks in the middle of tracing the azimuth tracks. Further, since a track from which an image signal is being reproduced is suddenly changed over to a track of a different azimuthal angle during the reproduction, variation of H occurs by a few H components at the moment when this change has occurred, which results in an occurrence of a fluctuation on the screen. It has also been difficult to correct this deviation of H as described above.